and Polymers 2008, Vol.9, No.6, 691-697

Probing of an Environmentally Friendly Regenerated Material Having Bimorphic Behavior

Woo Sub Shim*, Jae Pil Kim1, Jung Jin Lee2, Joonseok Koh3, and Ik Soo Kim4 Textile Engineering, Chemistry & Science Department, North Carolina State University, Raleigh, NC 27695-8301, USA 1Department of Materials Science and Engineering, Seoul National University, Seoul 151-742, Korea 2Fiber System Engineering Program, Division of Polymer System Engineering, Dankook University, Yongin 448-701, Korea 3Department of Textile Engineering, Konkuk University, Seoul 143-701, Korea 4SK Chemicals, Gyeonggi-do 440-745, Korea (Received December 18, 2007; Revised August 19, 2008; Accepted August 27, 2008)

Abstract: Novel regenerated cellulose material which was prepared from through the hydrolysis of acetyl groups have been developed by an environmentally friendly process without emitting toxic substances in addition to be at low production cost. They have composite crystalline structure constituted of cellulose II and cellulose IV. Also, they show a lamellar morphology with an increased amorphous region, as compared to conventional regenerated cellulose such as vis- cose and cupra rayon. Our data obtained by several independent methods demonstrated that the adsorption properties of cellulose fibers depend predominantly on the amorphous region. Keywords: Regenerated cellulose, Crystalline structure, Amorphous region, Viscose rayon, Cuprammonium rayon

Introduction in varying degrees by larger plants; on the average, 30-35 % is recovered, the balance being lost through volatilization or Cellulose is generally considered as being the most decomposition during the spinning process. Although efforts abundant and useful material, due to their excellent physical by the major producers are expected to reduce carbon properties such as its gloss, specific gravity, and comfortable disulfide, increasing environmental concern has centered on touch. Viscose rayon is a regenerated cellulosic fiber. The the conventional preparation of conventionally regenerated process involves dissolving wood pulp in an inorganic cellulosic fibers since still some amount of the remaining solvent containing sulfur and extruding the fiber. The Textile carbon disulfide and heavy metal ions need to be recovered Fiber Products Identification Act (TFPIA) defines rayon as in waste treatment facilities at the plant to meet established manufactured fibers composed of regenerated cellulose, as water pollution regulations [4]. well as manufactured fibers composed of regenerated Because of the demand for pleasant environment materials cellulose in which substituents have replaced the proton of without the release of pollutant, we developed a new the hydroxyl groups [1]. Rayon fibers are widely used in cellulose material using environmentally friendly process. It apparel, home furnishings, and industrial materials [2,3]. was prepared from the untreated, cellulosic diacetate fiber Unfortunately, it was found that the regenerated cellulose with a degree of substituent of 2.0 or higher by saponifying fibers produced by conventional processes caused harmful (at 70-130 oC and preferably at 80 oC) 75 % or greater of the environmental problem, posing their use in various total acetyl groups of the cellulose acetate fiber into applications to be diminished. In the typical manufacturing hydroxyl groups (Scheme 1) [5,6]. This new regenerated processes of these viscose rayon fibers, the raw material is cellulose material is claimed to offer environmental alkali cellulose with a high α-cellulose contents, which are advantages over other conventional regenerated cellulose prepared by treating wood pulp with an excess of sodium fibers because it does not emit toxic materials such as carbon hydroxide solution. The alkali cellulose reacts with the CS2 disulfide and heavy metal ions and enjoyed advantages of to form xanthate ester groups. The carbon disulfide also being very simple and low in production cost unlike reacts with the alkaline medium to form inorganic impurities conventional production methods of viscose rayon which which give the cellulose mixture a characteristic yellow use highly concentrated alkali solutions, carbon disulfide, color, and this material is referred to as yellow crumb. and sulfuric acid. The structure of the new regenerated

Because accessibility to the CS2 is greatly restricted in the cellulose was investigated by FT-IR, X-ray diffraction, and crystalline regions of the soda cellulose, the yellow crumb is birefringence measurement and its mechanical property and essentially a block copolymer of cellulose and cellulose dyeing properties were also determined in this study. xanthate. The raw materials such as sodium sulfate and zinc sulfide, which are used in the production of the rayon fibers, Experimental are subsequently recovered. But, carbon disulfide is recovered Materials *Corresponding author: [email protected] Viscose rayon fabric (plain weave, warp 82 filament/inch,

691 692 Fibers and Polymers 2008, Vol.9, No.6 Woo Sub Shim et al.

Scheme 1. Alkaline hydrolysis of cellulose acetate.

weft 62 filament/inch), cupra rayon fabric (plain weave, Warp 86 filament/inch, weft 58 filament/inch), and a new regenerated cellulose fabric (plain weave, warp 96 filaments/ inch, weft 56 filaments/inch) obtained from cellulose acetate fibers by alkali-hydrolysis [5,6] were supplied courtesy of SK Chemicals (South Korea) (Figure 1). The three dyes used were commercial samples that were not purified prior to use; Everdirect Supra Red BWS (C.I. Direct Red 243), Procion H-E3B (C.I. Reactive Red 120), and Cibanone Red 2B (C.I. Vat Red 10). A commercial sample of a fixing agent (Neofix RP-70C, a -based cationic resin) was supplied by Korea Fine Chemicals Co. (Daegu, Korea) for direct dyeing. A commercial sample of soaping agent (SNOGEN CS-940N, non-ionic) was supplied by Daeyoung Chemicals for reactive dyeing. Peregal P, used as a leveling agent, was supplied by BASF and Setamol WS, a dispersing agent, and Dekol SN, a soaping agent, were supplied by

Dae-Yang TexChem Co. Sodium hydrosulfite (Na2S2O4), used as a reducing agent and sodium hydroxide (NaOH) were purchased from Sigma Aldrich Chemicals Co. for vat dyeing. All other reagents were of general purpose grade.

Characterization FT-IR spectra were obtained with a Nicolet, Magna 7509 spectrometer using KBr pellet method to analyze new regenerated cellulose as well as viscose rayon and cupra rayon. Wide-angle X-ray diffraction (WAXD) was collected on a bundle of commercial viscose rayon, cupra rayon, and new regenerated cellulose at room temperature with a Bruker 2D-GADDS diffractometer using Cu-K radiation with λ = 1.5418 Å generated in a sealed Cu tube at 40 KV and 40 mA. Intensities were measured within the range of scattering angles (2θ ) of 3-33 o in the equatorial and meridional directions. The total scattering data was obtained by the summation of all the equatorial and meridional scattering data. The scattering data profiles were corrected for background and detector efficiency. The GADDS software integrated the intensity along each arc, making a correction for the effect of flat screen detection (unwarping), to create a one dimensional plot of intensity versus 2θ, Figure 1. Various cross-sections of the new regenerated cellulose; similar to a conventional powder-diffraction pattern. (a) fine filament (75d/50f), (b) Y-shape filament (75d/33f), and (c) Birefringence values (Δn) were obtained with a polarized hollow filament (45d/33f). microscope (Pol-12, Leica) having a 30 order Berek’s Regenerated Cellulose Having Bimorphic Behavior Fibers and Polymers 2008, Vol.9, No.6 693 compensator. The optical axis of a sample on the optical were tested either in dry state or in wet state at 25 ± 2 oC. stage of the equipment is detected by rotating the sample in Prior to testing in wet condition, all samples were the plane. The detected axis gives the solution that satisfies neutralized in 1 N NaOH for 15 min and rinsed thoroughly i2w = 0. In general, a positive birefringence (Δn > 0) indicates under tap. that the direction of the largest refractive index in the sample The dyeings were carried out using a laboratory dyeing plane corresponds to the stretching direction. On the other machine (Ahiba Spectradye Plus, Datacolor International) at hand, a negative birefringence (Δn < 0) means that the liquor ratio 30:1, commencing at 30 oC. The dyebath direction of the smallest refractive index in the plane temperature was raised 1 oC/min. The dyeing methods used corresponds to the stretching direction. are shown in Figure 2, and their structures are shown in The tensile strength and elongation were determined with Table 1. The fabrics dyed with direct, reactive, and vat dyes an extension rate of 10 mm/min by the universal tensile were rinsed and then treated with a fixing agent (2.5 % on testing instrument (RTM-1T, Yashima Works). Viscose the weight of fabric) for 15 min at 60 oC for direct dyeing rayon fiber (denier: 2.0 den, length: 51 mm), cupra rayon and treated with a soaping agent (0.5 g/l) for 30 min at 98 oC fabric (denier: 2.0 den, length: 51 mm), and a new for reactive dyeing and then treated with hydrogen peroxide regenerated (denier: 2.0 den, length: 51 mm) solution (30 % w/v) for 15 min at 60 oC and next they were

Figure 2. Dyeing profile for three different dyes. 694 Fibers and Polymers 2008, Vol.9, No.6 Woo Sub Shim et al.

Table 1. Structures of the dyes used in this study

Dyes Chemical structure Molecular weight (Mw)

C.I. Direct 1116.91 Red 243

C.I. Reactive 1144.82 Red 120

C.I. Vat 470.43 Red 10

soaped in the aqueous solution of 2.5 g/l Dekol SN for 15 structures of all the fibers are similar. All reflection peaks min at the boil for vat dyeing. can be indexed based on the known cellulose II crystal Color strength (K/S) of the dyed samples was measured structure [7]. The higher amorphous content and poor using a Datacolor Spectroflash SF 600 Plus-CT spectro- crystalline orientation of new regenerated cellulose fiber as photometer with following: illuminant D65, large area view, compared with viscose and cupra may arise from the specular component included, and CIE 1964 Supplemental saponification process of cellulose acetate which is achieved Standard Observer (10 degree observer) by using equation by immersing it in the aqueous alkaline solution at 80 oC (1). With each sample folded twice, reflectance was [5,6]. This may be due to the amorphous regions of the measured four times at different surfaces and averaged. cellulose diacetate fibers used as the starting material. As seen in Figure 3, the non-crystalline part was taken as K ()1 – R 2 ---- = ------(1) contributing to the intensity of the diffuse background and S 2R the crystalline peaks as contributing to the intensity of the where R is the reflectance of an infinitely thick layer of the selectively diffracted radiation (the peaks occurring on top material illuminated with light of a known wavelength, K is of the background). All the amorphous backgrounds and the the absorption coefficient, and S is the scattering coefficient. Bragg peaks were resolved by the curve fitting method. In The function of K/S is directly proportional to the all the data, we found three Bragg peaks at 2θ ≈ 12 o, 19 o, concentration of the colorant in the substrate. The fabrics and 22 o which are indexed as (110), (110), and (020) peaks were dyed with these dyes with 0.5, 1.0, 2.0, 4.0, and 6.0 % of cellulose II [7]. It has been known that conventional rayon o.w.f. dye concentration for evaluating the build-up property. fibers, such as viscose rayon, cupra rayon, Bemberg rayon, high tenacity rayon, and Fortisan have a crystalline structure Results and Discussion of cellulose II [8]. In Figure 3 (c), we found another peak 2θ ≈ 15.4 o which is (110) peak of cellulose IV phase [9]. The WAXD curves are shown in Figure 3 for the regular peak at 2θ ≈ 22 o was attributed to (020)/(200) peak of viscose rayon fibers (a), cupra rayon (b), and new cellulose IV which overlapped with (020) peaks of cellulose regenerated cellulose (c). All the data contained almost the II [7,9]. The coexistence of the Bragg peaks from cellulose II same features: an amorphous halo with several crystalline and IV for new regenerated cellulose indicates bimorphic Bragg peaks. Crystallinity can be determined from a wide- behavior of the crystalline structure. It was also suggested angle X-ray diffraction (WAXD) scan by comparing the area that the tensile properties of cellulose were affected by the under the crystalline peaks to the total scattered intensity. type of crystal structure. The intense amorphous halo in all the data indicates the Since most crystalline Bragg peaks of viscose rayon, existence of a significant amount of amorphous, disordered cupra rayon, and new regenerated cellulose fibers were phase. The numbers and positions of the Bragg peaks in all located in the region of 2θ ≤ 50 o, their approximate apparent the patterns are almost similar, indicating that the crystalline crystallinities were estimated based on the curve fitted data Regenerated Cellulose Having Bimorphic Behavior Fibers and Polymers 2008, Vol.9, No.6 695

Figure 4. FT-IR spectra of (a) cellulose diacetate, (b) viscose rayon, (c) cupra rayon, and (d) new regenerated cellulose.

shown in Figure 3. The estimated values of crystallinity were 36 ± 2%, 51± 2 %, and 28 ± 2 % for viscose rayon, cupra rayon, and new regenerated cellulose, respectively. The lower value of crystallinity of new regenerated cellulose can exhibit better solvent processing characteristics and dyeability. Figure 4 shows FT-IR spectra of cellulose acetate, viscose rayon, cupra rayon, and new regenerated cellulose. The deacetylation of the cellulose diacetate fiber was indentified through FT-IR spectra. In these data, the C-O strectching peak of the β-1,4-linked D-glucopyranose was read at 1160 cm-1 and the carbonyl band of the acetyl groups were read at 1760 cm-1 [10]. These FT-IR peaks were calculated by integration and the ratio between them was obtained. The large quantity of carbonyl groups in the acetate moieties produced the large peak at 1760 cm-1 in curve (a) corresponds to the untreated cellulose diacetate, whereas the carbonyl peak at 1760 cm-1 was greatly reduced and almost disappeared in curve (d). On the basis of the FT-IR data, it was confirmed that almost the entire acetyl group of the cellulose diacetate was substituted with a hydroxyl group and that the cellulose was completely regenerated by eco- friendly process. The measured tensile strength and elongation at the break of samples is shown in Figures 5 and 6. The samples were first tested in the dry state. For the new regenerated cellulose, the tensile strength was 1.27 (gf/den) and the Figure 3. Wide angle X-ray scattering pattern resolved into elongation was 35 %. They have lower tensile strength and individual integral intensities of the corresponding crystal planes higher elongation than viscose rayon (1.55 gf/den, 15.3 %) and the amorphous phase. ( ◀...... ) amorphous component, ( ◀ ------) and cupra rayon (2.63 gf/den, 13.2 %). Next, samples were crystalline component. tested in the wet state. The results showed a significant 696 Fibers and Polymers 2008, Vol.9, No.6 Woo Sub Shim et al.

Figure 5. The tensile strength of viscose rayon, cupra rayon, and new regenerated cellulose.

Figure 6. The elongation of viscose rayon, cupra rayon, and new regenerated cellulose. difference in the mechanical properties relative to the dry state. For the new regenerated cellulose, the tensile strength was 0.51 (gf/den) and the elongation was 42 %. They have a lower tensile strength and higher elongation than viscose rayon (0.65 gf/den, 21.5 %) and cupra rayon (1.56 gf/den, 32.2 %). Figure 7 shows build-up properties of three different dyes on viscose rayon, cupra rayon, and new regenerated cellulose. The build-up properties of the new regenerated cellulose are better than those of viscose rayon and cupra rayon for the three different dyes. The results show that new regenerated cellulose dyes to a much deeper shade than the other rayons. The dyeing properties of fibrous polymeric materials depend on the relative amount of amorphous phase and the chain packing, especially in the intermediate phase Figure 7. Build-up properties of three different dyes on viscose, between crystalline and amorphous phases. All the structural cupra, and new regenerated cellulose; (a) C.I. Direct Red 243, (b) parameters of solvent and dye molecules strongly affect the C.I. Reactive Red 120, and (c) C.I. Vat Red 10. sorption characteristics of fibrous polymers. Since the molecular orientation provides information on the degree of the birefringence measurement was conducted to measure chain packing in all the crystalline and intermediate phases, the degree of orientation of viscose, cupra, and new Regenerated Cellulose Having Bimorphic Behavior Fibers and Polymers 2008, Vol.9, No.6 697 regenerated cellulose materials. This resulted in a phase References difference or retardation (τ) as the light traverses the sample material. If the material is not dichroic, then the retardation 1. K. Kong, R. J. Davies, M. A. McDonald, R. J. Young, is related directly to its birefringence [11]. Birefringence M. A. Wilding, R. N. Ibbett, and S. J. Eichhorn, data, determined by a polarized microscope, were found to Biomacromolecules, 8, 624 (2007). support the WAXD results; birefringence of viscose rayon 2. S. Klahorst, A. Kumar, and M. M. Mullins, Text. Chem. (0.036) and cupra rayon (0.038) was higher than that of new Color., 26, 13 (1994). regenerated cellulose material (0.019). These results mean 3. F. Jones in “The Theory Coloration of Textiles” (A. the chain packing of viscose rayon and cupra rayon is better Johnson Ed.), pp.405-409, Society of Dyers and Colourists, than that of new regenerated cellulose fiber, which points out Bradford, 1989. poor dyeability [12]. 4. K. Bredereck and F. Hermanutz, Rev. Prog. Coloration, 35, 59 (2005). Conclusion 5. I. S. Kim, J. S. Ahn, and B. H. Kim, Kor. Patent, 0015443 (2000). We investigated new environmentally friendly regenerated 6. I. S. Kim, J. S. Ahn, and B. H. Kim, U. S. Patent, 6361862 cellulose which has coexisting cellulose II and IV prepared (2000). by saponifying at least 75 % of the total acetyl groups of a 7. F. Kolpak and J. Blackwell, Macromolecules, 9, 273 cellulose acetate fiber with a degree of substitution of 2.0 or (1976). higher into hydroxyl groups. The mechanical property is 8. W. E. Moriton and J. W. S. Hearle, “Physical Properties of found to be similar to those of already commercialized Textile Fibers”, pp.84-94, Butterworth, London, 1962. viscose and cupra rayon and dyeing property is slightly 9. E. S. Gardiner and A. Sarko, Can. J. Chem., 63, 173 better than those of other regenerated cellulose. (1985). 10. A. Carrillo, X. Colom, J. J. Sunol, and J. Saurina, Eur. Acknowledgements Polym. J., 40, 2229 (2004). 11. R. M. A. Azzam and N. M. Bashara, “Ellipsometry and The authors appreciate the financial support from the Polarized Light”, pp.52-67, North Holland, Amsterdam, Graduate Student Support Plan (GSSP) in the college of 1979. Textiles, NC State University, USA and the Ministry of 12. J. Koh, I. S. Kim, S. S. Kim, W. S. Shim, and J. P. Kim, Commerce, Industry and Energy, South Korea (Support for Fiber. Polym., 5, 44 (2004). Industrial Technology Development Program, No. D11-08- 007).